Electron spin resonance of the Mn2+ ion in the study of the mobility of water adsorbed on silica gel and γ-alumina

Abstract

The electron spin relaxation of Mn²⁺ in supercooled water adsorbed on silica gel and γ-alumina has been investigated. The correlation time for the modulation of the zero-field splitting tensor has been evaluated from the temperature and frequency dependence of the e.s.r. linewidth: τ_c= 1.4 ± 0.3 × 10^–12 s at 25 °C has been extrapolated for bulk water solution. In the capillary adsorbed water, lineshape analysis suggests the existence of a distribution of crystal-field sites. The rate of interchange among differently relaxing sites is < 10⁹ s^–1. This suggests a long-range solid-water interaction which slows the mobility of water molecules up to 15–20 Å from the surface.